Disk drives, also called disk files, are information storage devices that use a rotatable disk with concentric data tracks containing the information, a head or transducer for reading and/or writing data onto the various tracks, and an actuator connected to a carrier for the head for moving the head to the desired track and maintaining it over the track centerline during read and write operations. The most common form of actuator is a rotary voice coil motor (VCM) actuator that moves the head carrier in a nonlinear, generally arcuate path across the disk. There are typically a number of disks mounted on a hub that is rotated by a disk drive motor, and a number of head carriers connected to the actuator for accessing the surfaces of the disks. A housing supports the drive motor and head actuator and surrounds the heads and disks to provide a substantially sealed environment. In conventional magnetic recording disk drives, the head carrier is an air-bearing slider that rides on a bearing of air above the disk surface when the disk is rotating at its operational speed. The slider is maintained next to the disk surface by a biasing force from a suspension that connects the slider to the actuator.
In contrast to conventional air-bearing disk drives, contact or near-contact disk drives have been proposed that place the head carrier in constant or occasional contact with the disk or a liquid film on the disk during read and write operations. Examples of these types of disk drives are described in IBM's U.S. Pat. No. 5,202,803 and published European application EP 367510; U.S. Pat. No. 5,097,368 assigned to Conner Peripherals; and U.S. Pat. No. 5,041,932 assigned to Censtor Corporation.
Disk drives are sensitive to external shock and vibration that can cause the heads to move to the wrong track during a track accessing or "seek" operation or to move off track during a read or write operation. The writing of data on the wrong track is unacceptable because it usually results in the loss of data on the track that is written over. Various techniques have been proposed to address this problem by sensing the external force and either compensating for it or shutting down some operation of the disk drive until the force is removed. These techniques typically involve the use of conventional accelerometers mounted to the disk drive housing. European published patent application EP 264535, assigned to Hewlett-Packard, describes a disk drive that uses accelerometer output as feedback into the actuator tracking control or servo system to compensate for shock or vibration-induced tracking errors. Japanese published patent application JP 03-252962, assigned to NEC Corporation, describes a disk drive that uses accelerometer output to move the heads to a parking zone and stop rotation of the disk drive motor when the accelerometer output exceeds a predetermined value.
As disk drives become smaller and their track density (i.e., number of data tracks per radial inch) increases, the effect of external shock and vibration becomes more pronounced. This is especially true in rotary actuator disk drives when the external force is in a direction that would cause the actuator to rotate. What is needed is a disk drive having a sensing device that produces a more rapid and reliable response than conventional accelerometers to external forces to maintain the heads on track and/or inhibit the writing of data on the wrong track.